As has long been known, high speed torque transmission can result in premature failure of a drive shaft and/or coupling where operation above the transmission limits of a drive train or deviations caused by flexing of one or several members of the train that are coupled takes place which goes uncorrected for a period of time. In the past, measurement of torque, deflection and other conditions of a rotating shaft has usually involved the placement of interengaging toothed elements such as exciter wheels on the shaft together with a sensor which may be optical or magnetic and which is responsive to the spacing or change in spacing between the teeth of exciter wheels that are placed on the shaft. Devices representative of the prior art will be found in U.S. Pat. Nos. 3,587,305; 3,543,649; 5,228,349 and 5,440,761.
While the devices of the foregoing patents have provided adequate measurement of torque caused deflections that occur in a rotating shaft, they increase the weight of the coupling by a significant amount and have adverse effects on the system rotor dynamics.